Exemplary embodiments relate to a method of operating a nonvolatile memory device.
A nonvolatile memory device has a characteristic in which data stored therein are not lost even though power is not supplied. A representative nonvolatile memory device is a flash memory device. There are basically two types of flash memory devices, a NOR type flash memory device and a NAND type flash memory device, according to the structure of the flash memory cell array. The gate of a flash memory cell is configured to include a tunnel dielectric layer, a floating gate, a dielectric layer, and a control gate.
In a nonvolatile memory device, a program operation and an erase operation are performed through F-N tunneling. During the program operation, electrons are accumulated in the floating gate, and during the erase operation, electrons accumulated in the floating gate are discharged toward a substrate. During a read operation, a threshold voltage of a memory cell, varying according to the amount of electrons accumulated in the floating gate, is detected, and data stored in the memory cell are determined according to a level of the detected threshold voltage.
Although the nonvolatile memory device retains its data without the supply of power, the data may be retained in a programmed state for a long period of time, or a threshold voltage of a memory cell may shift due to a baking process upon fabrication. Such a characteristic is called the retention characteristic. The error rate of data, stored in the nonvolatile memory device for a long period of time, can be increased according to the retention characteristic.